Positioning and/or angle control devices have many uses in the motor vehicle technique, e.g. as adjusting devices for clutches, for the control of oil flows, as set value sensors for actuators in steering systems, for an adjustment of active shock absorbers and for control of the adjustment of the speed ratio of transmissions such as continuously variable toroidal drives or continuously variable transmissions (CVT transmissions).
As positioning and/or angle control devices units are often used which does not make possible a detection or feedback of the absolute position, e.g. in stepping motors. But since this absolute position becomes necessary for the use of control and regulation strategies, there have been already used among others the following possibilities:
a) external, separate measurement or detection of the absolute position; PA1 b) continuous incremental detection occasionally, regularly, or at specific moments (e.g. initializing) of the absolute position in certain prominent positions (stops, additional/missing transmission detection among others); PA1 c) continuous incremental detection by taking into account the position departing from the set nominal value and detection of the absolute position like in b); PA1 d) determination from other detected system factors; this is possible only when a clear, sufficiently precise relationship exists; PA1 e) a combination of the above methods.
For stepping motors a method according to c) is generally used (see also the publication of the firm Motorola Inc., 1990 "TPU Time Processor Unit Reference Manual", chapter 3, page 103). In this initializing method described therein for a stepping motor, the latter is transferred from its momentary position to a preset basic position corresponding to a firm stop.
Especially in the motor vehicle technology it must be ensured that the divergences of the calculated from the real position (called "step errors" in stepping motors), which appear during the operation between the moments of the absolute position detection do not exceed an admissible measure. Such step errors can result, e.g. from the fact that due to vibrations high counterforces result which cannot be overcome by the electromotive force of the stepping motor associated therewith is important, since thereon directly depends the accurate control of the part, e.g. the adjustment of the reduction ratio of a continuously variable transmission in a motor vehicle. Incorrect adjustments of the speed ratio can result in too high or too low numbers of revolutions of the motor and therewith comfort impairment and also elevated fuel consumption. Besides, no adjusting power should act during stoppage on the continuously variable toroidal drive, since this can lead to mechanical damage.